Bat Colonies Overwhelming Australian Gardens

Elizabeth M. Tasker for National Geographic News

October 29, 2002

The demand for real estate in Sydney and Melbourne is at an all-time
high, and not just among people. The grey-headed flying fox, a large
Australian bat that feeds on fruit and nectar, has established permanent
"camps" in the botanical gardens of both cities.

The thousands of flying foxes living year-round in the oldest groves in both gardens are stripping leaves and breaking branches, damagingand even killingsome of the trees.

Both bat camps are increasing in size, escalating the need to find ways to minimize damage to the Royal Botanic Gardens in Melbourne and Sydney. At the same time, the Australian government has classified the grey-headed flying fox as a vulnerable species, as its numbers decline throughout much of the country.

This dilemmahow to save the bats and also protect the gardenshas conservationists and arborists searching for solutions.

Real-Estate Connoisseurs

Grey-headed flying foxes are normally a nomadic species, moving through the landscape as the seasons change and food becomes available.

Flying foxes have always been drawn to Sydney's center. There are reports dating as far back as the 1850s of the bats trying to colonize the botanic gardens. But it wasn't until the 1980s that they were allowed to stay.

The bats camp in the trees; during the day up to 9,000 of them can be seen hanging upside down on branches like some sort of bizarre hairy screeching fruit. At dusk they stream out of the gardens by the thousands to feed on fruit trees and eucalyptus flowers throughout the city's suburbs.

The grey-headed flying foxes also moved into the botanical gardens in Melbourne during the 1980s. Previously, they had shown little interestflying foxes are essentially tropical mammals, and the temperatures were too cool for them.

However, the city has grown warmer. The growing lack of vegetation and extensive paved developmentroads, sidewalks, parking lots, and buildingshave created a phenomenon known as the "urban heat island effect."

A recent study by ecologist Mark McDonnell, director of the Australian Research Centre for Urban Environments, suggests that this situation has contributed to the flying foxes taking up permanent residence in the city.

The Melbourne colony now has 5,000 permanent year-round residents, and swells to 20,000 bats in summer. It is the only breeding colony of flying foxes in the state of Victoria, and the southern-most colony in the world.